The invention relates to a process according to the preamble of claim 1.
Intermediate cooling in the compressor of a gas turbine set is a well-known measure which can substantially contribute to an increase of the efficiency factor and the performance of a gas turbine set, particularly when the heat removed from the partially compressed working medium can be usefully employed at a place in the power station. EP 515 995 proposes in this regard to conduct the compressor air through a steam generator, and thus to produce an amount of steam which can be further used in the water-steam circuit of a combination plant. EP 781 909 and EP 898 645 propose supersaturating the air with water at the compressor inlet, so that a binary air-water-steam mixture enters the compressor. The successive evaporation of the water droplets introduced into the compressor leads to an intensive internal cooling of the compressor; the resulting steam is expanded in the turbine of the gas turbine set, with delivery of power.
Besides a significant reduction of the power uptake of the compressor, the result of a simple consideration of stage kinematics of the compressor is that the intermediate cooling furthermore leads to a displacement of the pressure build-up in the rear compressor stages. The article, xe2x80x9cWet Compression: Gas Turbine Power Output Enhancement for Peak-Load Demandxe2x80x9d, Siemens Power Journal 1/2000, pages 29-32, states in this regard that this leads to a disequilibrium between the compressor bleed pressures for the cooling air and the turbine pressures which correspond to these. It is proposed on the one hand to correspondingly adjust the diaphragms built into the cooling system for cooling air mass flow adjustment. Alternatively, it is proposed to provide an automatic cooling air regulating system.
With regard to the first proposed variant, it is to be stated in this connection that this leads, in operation without compressor cooling, to a cooling air mass flow which is far above what is required, markedly limiting the power and efficiency factor potentials of the gas turbine set. With regard to the second proposed variant, it is to be stated that the document gives no hint as to how such a control system would be implemented.
The present invention has as its object to provide a process for regulating the cooling air supply of a gas turbine set, avoiding the disadvantages of the state of the art.
This is attained by the totality of the features of claim 1.
The core of the invention is thus, on the one hand to provide the cooling system of a gas turbine with suitable means which make possible a targeted external influence on the cooling air mass flow which flows there, and to control these means in dependence on a suitable operating parameter. This operating parameter contains, in one embodiment, which in particular finds application in variable compressor cooling, principally magnitudes which decisively affect or directly reproduce the pressure distribution and the mass flows in the cooling air system, or respectively around the cooling air system. The operating parameter can furthermore contain magnitudes which supply a measure for the hot gas temperature in the region of the components to be cooled, or for the material temperatures of critical components. The two can also be combined in a suitable manner.
It is to be stated that the process according to the invention is in no way limited to the compensation of fluctuations of the pressure conditions in the cooling system due to different compressor cooling. Likewise, the described process can also find application in order for different load states or thermal loading of critical components to be fulfilled. The process can also be used in dependence on the fuel used or on pressure losses in the main flow path of the gas turbine set: the combustor pressure loss is particularly to be named. This enumeration is to be understood as in no way final, as will be explained hereinafter and also using the embodiment examples.
It is known from EP 1 028 230 to determine a cooling air mass flow by means of a diaphragm measuring point integrated into the cooling air system, and to adjust an adjustable throttle point to a reference mass flow. However, it is found that, precisely in operation with stronger cooling of the flow in the compressor, a control in dependence on cooling air mass flow alone does not give the best result in all circumstances.
A preferred variant of the invention consists in relating the cooling air mass flow to the compressor inlet mass flow. The cooling power in the compressor can then furthermore also be considered as a measure for the shift of the pressure buildup, in a manner which is suitable and which depends on the specific data of the compressor.
The cooling power in the compressor can be determined among other things and in a particularly simple manner by sensing the temperature difference over an intermediate cooler.
The cooling power can also be considered by calculating a supersaturation of the intake air from the ambient conditions, i.e., ambient temperature, pressure and humidity, and also from an amount of water introduced into the supply flow upstream of the compressor inlet.
If water is introduced within the compressor for evaporative cooling, this amount of water can also be made use of as a measure for the cooling power.
This cooling power can be made use of alone or in combination with other magnitudes for forming the operating parameter.
When the mode of determination of the operating parameter is spoken of in this context, this does not at all mean that yet other magnitudes cannot enter into the calculation of the operating parameter besides the explicitly mentioned magnitudes.
A further magnitude which is to be considered in the formation of the operating parameter is the setting of compressor guide blade rows and/or of an adjustable front guide row. The latter is particularly important in the calculation of a compressor inlet mass flow.
A further possibility for forming the operating parameters which is in general easily accessible is to relate the cooling air pressure, i.e., the pressure in the compressor at the place of cooling air bleed, to the compressor outlet pressure or to a further pressure which supplies a reference value for the outlet pressure of the cooling air. This relationship also can be made use of alone or in combination with other magnitudes for forming the relevant operating parameters according to the invention.
Furthermore, the combustor pressure loss can also be made use of for the formation of the operating parameter relevant to the process.
The enumeration of possible combinations for the formation of an operating parameter for the control of the cooling air mass flow is not to be taken as final; depending on the specific circumstances, where the compressor characteristic, the location of cooling air removal, and the kind of compressor cooling possibly implemented, are particularly to be considered; other magnitudes will of course be readily recognized by the skilled person as relevant, and will be considered in the formation of the operating parameter.
The thermal loading of the components to be cooled can be determined by means of a parameter which in particular includes a turbine inlet temperature, a turbine outlet temperature, an amount of fuel, an air mass flow, and/or the compressor outlet pressure, alone or in combination with each other or with other magnitudes.
An advantageous embodiment can be seen in that a turbine inlet temperature, determined in a manner known per se, is to be multiplied by a compressor outlet pressure and related to a cooling air initial pressure, where machine-specific multiplicative factors and exponents are to be used for the individual magnitudes.
In a specific case, the available instrumentation and the accessibility for measurement techniques of a gas turbine set are decisive for the formation of the operating parameter.
The cooling air mass flow can be set either by influencing the flow directly in the cooling air channels, or by influencing a bypass bypassing a throttle point of a cooling air duct of the cooling air system. The influence can be effected here by providing a variable throttling, or by providing means for amplifying the flow with an adjustable driving force. The latter takes place, for example, and with advantage, in that a working fluid inflow to ejectors acting on the cooling air duct or on the bypass is adjusted.
Finally, a supply of an additional fluid downstream of a throttle point arranged in the cooling air duct, for example, an amount of steam taken from a waste heat steam generator, can be controlled in dependence on the selected operating parameter.
In a gas turbine having a high pressure cooling system and at least one cooling system of at least one lower pressure stage, hereinafter termed high pressure and low pressure cooling systems respectively, the invention is implemented in particular in the low pressure cooling system. Then above all, when the gas turbine is operated with variable compressor cooling, the pressure relationships vary strongly in the low pressure cooling system which is indeed supplied with air taken from an intermediate compressor stage, so that an influence on the cooling air mass flow in the low pressure cooling system is particularly advantageous.
An operating parameter constructed according to the invention can furthermore also find application for the control of the variable compressor guide row proposed in DE 199 07 907, the cooling air amount likewise being thereby influenced in the end.